Most people on this planet have religious beliefs, that claim some behaviors are good, and some behaviors are bad. A lot of them don't make much sense. Maybe you think that God doesn't want you eating bacon. Why? I don't know. But you follow them because you believe that's what God wants you to do. A lot of people—millions and millions of people in the US—believe that their God disapproves of gay marriage. And so these people, who are trying to understand the world and their place in it, try to live out the expectations they believe that their God has for them.
Maybe you think that sucks. Well, in fairly short order, gay marriage is being legalized over their objections. That's a good thing. But to believe that it's being fueled by sociopathic animosity—to turn millions of Americans into movie villains because they haven't yet learned what you already have—is an act of arrogant blindness. And it's a harm to you as well—by not understanding why they believe what they do, by turning them into fictional caricatures, you lose all hope of changing their mind, and helping them learn what you learned.
I have no doubt that, over time, quite a lot of them will see the errors of their ways, and support gay marriage. But it will be despite you, not thanks to you.
That's not what the first amendment says. A lot of laws have inspiration in religion (and tradition)—people believe X, and so want laws that support X. But if X gets passed as a law, it's because people support X, not necessarily because it comes from a religion. What we're seeing with gay marriage is, people are studying the matter, and finding out that the only reasons against it are religion, and tradition. And those aren't sufficient. So laws against it are being overruled.
But that isn't to say that religion has (or should have) no influence, because it influences the believers, who then support laws & lawmakers. Nor is always it possible to separate the beliefs that someone holds for religious reasons, vs. beliefs they hold for other reasons. But it does mean that a law needs more than religious reasons to stay on the books. Thankfully, gay marriage seems to be one that is mostly held for religious reasons, so laws preventing it can be dismantled (versus, say, marijuana prohibition. It's more than just religion, so it's harder to dismantle).
But if all you take away is that people against gay marriage aren't driven by sociopathic malice, then that's still an improvement.
If that's your understanding of people who vote against gay marriage, then you really have no idea what's going on in this country.